Shaun Marsh played well during the first Test at Centurion but needs to be examined thoroughly by the South African attack. Photograph: Alexander/AFP/Getty Images

Dear South African cricket team,

For most of the past five years, you have been the best Test team in the world. You have earned that No1 ranking and my unstinting admiration. Therefore, I am writing to you to aid you in your noble efforts to shed your tag as choke artists extraordinaire.

Now, I can’t help you counteract the Australian bowlers — our pace battery consists of the choicest pickings of arguably the finest crop of quicks that Australia’s ever produced and our off-spinner, still only 26, is well on track to becoming our most successful Test finger-spinner ever.

What I can help you with is one of our key batsmen. Before this series, your astute countrywoman, Antoinette Muller, wrote of “Australia’s batting underbelly”. That underbelly is still there and, if you play your cards right, you can make it look like the sashimi-grade, line-caught southern bluefin tuna that it is.

The vulnerable link in the Australian batting line-up that you have, thus far, conspicuously failed to target in a remotely competent fashion is the No4: Shaun Marsh. He’s the last man protecting our captain and best batsman, Michael Clarke. Now, I’m a Clarke believer and always will be. I backed him even when national opinion polls said that he was one of the most unpopular Australian cricketers in living memory. The man is class. But, if he has a minor weakness, it’s against the new ball, which is why he has enjoyed so much success batting at five.

In order to get Clarke in early against the new ball, you’ll have to remove Marsh quickly – something that you failed to do in the first Test where Marsh comfortably scored a cumulative total of 192 runs against you.

How you contrived to fail to do that is utterly beyond me.

Marsh is 30-years-old. Before the Centurion Test, in a first-class career spanning nearly 13 years, he’d only managed eight first-class hundreds and his career first-class average stood at 35.02. He’d been averaging 24 in first-class cricket since September 2012. He once averaged 2.83 in a four Test home series against quite possibly the worst Test bowling attack ever to reach Australian shores. On Australia A’s tour of South Africa six months ago, he averaged 13.25 in two first-class matches against South Africa A. A batsman doesn’t compile a record as consistently mediocre as that unless he has some serious deficiencies in his game. Let me clue you in on a few of them.

Firstly, without a trigger movement, Marsh’s feet frequently resemble a pair of bridge pylons early in his innings. This, as you saw when you finally got him out in both innings of the Centurion Test, predisposes him to nick balls of a good length, or a touch shorter, between the off and fifth stumps. That is precisely how your quicks should bowl to him all the time. If you consistently bowl that line-and-length to him, then it is likely that, as AB de Villiers pointed out, he’ll glove or nick it like he did in his first innings at Centurion. Therefore, it is imperative that you populate the slips, gully and point regions with your best catchers. You may wish to consider stationing someone other than a career bat-pad at the key position of gully.

Marsh has his strengths too. Like all sons of the hard, sun-baked Western Australian soil, he’s extremely strong square of the wicket. Do not bowl him anything short and wide — he’ll cut you for four. He’s also a strong puller of the ball, therefore, generally refrain from bowling him bouncers. That being said, he has a long history of back, hamstring and calf problems and, like pretty much every batsman in history, he is vulnerable to the perfect throat ball. Therefore, bowl him the odd bouncer, especially when he’s new to the crease, but make sure that it’s a good one directed at his throat.

Marsh may have a consistently inconsistent first-class, Test and ODI record, but he has built one of the best T20 records of any opening bat in history. As such, he devours solid limited-overs finger spinners for breakfast on his way home from the pub. Therefore, do NOT – like you did in the second innings at Centurion – bowl Robin Peterson at him early in his innings.

Come to think of it, don’t bowl Peterson at Marsh or any of the Australian batsmen at all. With the notable exceptions of Clarke and Steve Smith, all the Australian batsmen have problems starting against world-class spin. But I’m sorry to tell you that Robin Peterson is not a world-class spinner. He’s a normally solid limited-overs finger-spinner who, based on his performance at Centurion, appears to have lost his primary attribute as a bowler – his control. Given that, on current form, Duminy’s finger-spin is no worse than Peterson’s, you might as well deploy Duminy as your spinner in Port Elizabeth and drop Peterson for an extra specialist batsman – you’re going to need him.

With that advice, it’s unlikely that Marsh will get in. If he does, don’t panic. It will look as if Seal Team 6 couldn’t dislodge him from the crease. But Marsh, as his record proves and you saw with your own eyes in the first-innings at Centurion, has the occasional brain fade even when he’s set. In general, it’s best to just keep boring away at him with balls of a good length, or a touch shorter, between the off and fifth stumps. However, if he gets in, you may wish to give him the odd short ball to pull or cut in the air. He may well hit it to a fielder like he did in the first-innings at Centurion. Don’t drop it.

You may be wondering why an Australian is writing to you in order to ostensibly help you. Fear not – this is not some cunning Australian plan, it is simply a happy scenario where the long-term interests of Australian cricket and the short-term interests of South African cricket neatly align. If Marsh is indeed the Test batting saviour that the Australian selectors believe him to be then we need to conclusively determine that as soon as possible and the only way to do so is test him to the very limit of his ability in the Test arena. I am writing to you to ensure that you do that. If Marsh turns out not to be Australia’s Test batting saviour, then, in light of his age and the alarming signal broadcast by his selection, it is in the long-term interests of Australian cricket that he be dropped as soon as possible.

Good luck in Port Elizabeth. And don’t forget your titanium boxes, Mitch is in a bit of form.